Low-energy excitations of the Hubbard model on the Kagom\'e lattice

The Hubbard model on the Kagom'e lattice is investigated in a metallic phase at half-filling. By introducing anisotropic electron hopping on the lattice, we control geometrical frustration and clarify how the lattice geometry affects physical properties. By means of the fluctuation exchange (FLEX) approximation, we calculate the spin and charge susceptibilities, the one-particle spectral function, the quasi-particle renormalization factor, and the Fermi velocity. It is found that geometrical frustration of the Kagom'e lattice suppresses the instability to various ordered states through the strong reduction of the wavevector dependence of susceptibilities, thereby stabilizing the formation of quasi-particles due to the almost isotropic spin fluctuations in the Brillouin zone. These characteristic properties are discussed in connection with the effects of geometrical frustration in the strong coupling regime.